Stabilized peptone solutions and plating baths containing the same

ABSTRACT

INVENTION RELATES TO THE STABILIZATION OF PEPTONE SOLUTIONS BY THE ADDITION THERETO OF A STABILIZING EFFECTIVE AMOUNT OF AN ADDITIVE COMPOUND SELECTED FROM CARBOXYLIC ACIDS, ESTERS OF SUCH ACIDS, KETONES, ALCOHOLS, ALKEHYDES AND THE LINEAR AND CYCLIC POLYMERS THEREOF AND THE USE OF SUCH STABILIZED PEPTONE SOLUTIONS IN THE ELECTRODEPOSITION OF METALS FROM PLATING BATHS CONTAINING SUCH STABILIZED PEPTONE SOLUTIONS.

United States Patent STABILIZED PEPTONE SOLUTIONS AND PLATIN G BATHS CONTAINING THE SAME Nicholas J. Spiliotis, Parsippany, N.J., assignor to Allied Chemical Corporation, New York, N.Y. No Drawing. Filed Nov. 20, 1968, Ser. No. 777,477 Int. Cl. C23b 5/10, 5/14, 5/46 US. Cl. 204-43 18 Claims ABSTRACT OF THE DISCLOSURE Invention relates to the stabilization of peptone solutions by the addition thereto of a stabilizing efiective amount of an additive compound selected from carboxylic acids, esters of such acids, ketones, alcohols, aldehydes and the linear and cyclic polymers thereof and the use of such stabilized peptone solutions in the electrodeposition of metals from plating baths containing such stabilized peptone solutions.

In the electrodeposition of metals such as zinc, copper, cadmium, tin, lead and mixtures thereof, aqueous plating baths are used as electrolytes in the plating of such metals on substrates by passing an electric current between an anode composed of the metal to be deposited and a cathode, which comprises the article to be plated. Both the anode and cathodes are immersed in the electrolyte which contains the metal to be deposited. These plating baths generally are either alkaline or acid, depending upon the components present. Under the influence of an electric current the metal anode is dissolved and deposited from the electrolyte on the article to be plated. By adjusting the pH of the electrolyte, the current density employed and components of the plating, the plating characteristics achieved on the article vary considerably.

In the deposition of metal deposits there sometimes occurs the development of protuberances, known as sprouts or trees, on the metal deposits. Since the space in between each anode and cathode in electrolytic cell is rather small, it is easy for these sprouts or trees, if they form on the cathode, to make contact with the neighboring anode, thereby causing a short circuit. When this occurs further deposit of the metal on the cathode is hindered until the short circuit is broken and both cell voltage and overall cathode current density in the cell re-established. Even if no short circuit develops the formation of a rough cathode deposit is accompanied by small pockets of electrolyte which cannot be washed out and thus an imperfect deposit of metal results. Generally, addition agents which usually are complex organic compounds or mixtures of such compounds are incorporated in the electrolyte to insure the formation of a smooth and dense metal deposit. A great many addition agents have been tested for use in preventing the development of these projections on the metal surface and in general the addition of a peptone solution, a proteinaceous electrophilic-type colloid, to the electrolyte has been found effective to prevent the formation of these sprouts or trees. A further effect sometimes found by the addition of the peptone solution is to improve the appearance of the electrodeposit, e.g., increasing the throwing power (ability to plate deposit in recesses), inhibiting the formation of dark colors and obtaining a certain degree of brightness in the plated product.

However, it has been found that in the use of a peptone solution the results achieved are not entirely consistent due to a problem which has been traced back to the preparation of the peptone solution. In many instances poor deposition of a metal from an electrolytic plating bath containing a peptone solution is the result Patented Mar. 7, 1972 of the improper preparation of the peptone solution. The method of dissolving the peptone is quite important and each plating shop has its own expert.

It has been the constant complaint that the preparation of this solution is time consuming and often prone to error in the hands of many platers who do not have such experts. If the peptone is not properly handled, the resulting solution may precipitate when added to the plating bath or cause roughness and striations in the deposit with subsequent loss of throwing power. It was felt that a prepared peptone solution would be a beneficial item for the electroplater. However, a drawback in the uniform preparation of a peptone solution for use in the electrodeposition of metals by a manufacturer is the fact that peptone solutions upon standing decompose within a relatively short period of time due to bacterial degradation. Thus, decomposed peptone solutions are ineffective to prevent the formation of sprouts or treeing of the metal deposits.

Peptone, an intermediate product in the hydrolysis of protein is a mixture of proteose and amino acids and resembles polypeptides and are generally prepared by the action of pepsin on albuminous bodies. Thus, being an intermediate in the hydrolysis of a protein, peptone has a tendency to decompose upon standing for relatively short periods of time. It is believed that the degradation products are skatole, putrecin, cadaverin, and the like which are quite toxic. It has now been found that peptone solutions suitable for addition to metal plating baths for the electrodeposition of metal can be prepared by adding to the peptone solution a stabilizing effective amount of at least one compound having the following structures:

wherein n is an integer from 1 to 10, preferably 1 to 3; R is either hydrogen or a hydrocarbon radical (aliphatic, straight, branched, or cyclic, saturated or unsaturated, substituted or unsubstituted) of from 1 to 6, preferably 1 to 4, carbon atoms; and R is either a hydrocarbon radical of from 1 to 6, preferably 1 to 4, carbon atoms or OR; R is a hydrocarbon radical of from 1 to 6, preferably 1 to 4, carbon atoms; and R is either R R2O R2 and R2-OR2OR2.

The additive compounds capable of stabilizing peptone solutions include carboxylic acids; esters of carboxylic acids; ketones, alcohols; aldehydes and their linear and cyclic polymers.

Illustrative of suitable carboxylic acids are the saturated aliphatic acids such as formic, propionic, butyric, petanoic and the like; dibasic acids such as oxalic, sebacic and the like; unsaturated acids such as acrylic, vinyl, acetic, maleic and the like; substituted acids such as malic, lactic, citric, tartaric, pyruvic, glycine, chloroacetic and the like.

Illustrative of suitable ketones are the saturated aliphatic ketones, such as acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and the like; the unsaturated ketones such as methyl vinyl ketone, ethylidene acetone, allylacetone and the like; the cyclic ketones such as cyclopentanonc, methyl cyclopentyl ketone and the like; substituted ketones such as monobromoacetone, acetol, methyl glyoxal and the like.

Illustrative of suitable alcohols are the saturated aliphatic alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, amyl and hexyl alcohols; the cyclic alcohols such as cyclohexanol and the like; the unsaturated alcohols such as allyl alcohol, methyl vinyl carbinol, allyl carbinol and the like; and the above alcohol substituted, for instance, with a halogen, amino group and the 'like.

Illustrative of suitable esters are the reaction product of the above-mentioned acids and alcohols such as, for instance, the reaction product of propyl alcohol and acetic acid, i.e., methyl propionate and the like.

Illustrative of suitable ethers are the saturated aliphatic ethers, such as dimethyl ether, diethyl ether, dipropyl ether and the like; the unsaturated ethers, such as methyl vinyl ether and the like; substituted ethers, such as alphachloromethyl ether and the like.

IIIustrative of suitable aldehydes capable of stabilizing the peptone solution are the saturated aliphatics aldehydes, such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde; the unsaturated aldehydes such as acrolein, crotonaldehyde and the like; polymers of these aldehydes, such as the linear and cyclic polymers of the lower alkyl aldehydes, i.e., paraformaldehyde (a polymer of formaldehyde), paraldehyde (a polymer of acetaldehyde), trioxane (a cyclic trimer of formaldehyde) and the like.

It has been found that the peptone solutions may be elfectively stabilized against decomposition for long periods of time by a peptone solution comprising an aqueous solution containing 50 to 500 grams per liter peptone; 2 to 100 ml. per liter of the stabilizing compound, and water up to one (1) liter. Preferably, the peptone solution comprises 250 to 350 grams per liter peptone, 5 to 50 ml. per liter stabilizing compound, and water to one liter. It has also been found desirable to add to the stabilized peptone solution minor amounts of fluoboric acid, e.g., from about 1 to 100 ml. per liter, preferably 1 to ml. per liter.

A convenient method for preparing the stabilized peptone solutions of the present invention may be conveniently achieved by adding to a suitable vessel approximately the required amount of water to make up the desired volume of solution. To this water, approximately /2 the required amount of stabilizing additive is added which prevents subsequent peptone decomposition and acts as an anti-foaming agent. The temperature of the aqueous solution may be raised to approximately 70 to 180 F., preferably 145 to 170 F. to aid in dissolving the peptone in the water. Overheating should be avoided to accelerate peptone decomposition. To this heated aqueous solution peptone is added in increments of of the amount desired to achieve fast dissolution of the peptone. Subsequent increments are added when the preceding amount of peptone is dissolved. The temperature is maintained at this level while constantly stirring the peptone solution until all of the peptone is dissolved. The solution is permitted to cool to room temperature, after which the remaining portion of stabilizer compound is introduced into the solution. If fluoboric acid is also to be added, it is at this time that the fluoboric acid is mixed into the solution. The volume of the stabilized peptone solution is then brought up to the desired level. The solution is then permitted to sit for a period of time, e.g., 24 hours, to allow any precipitate to form after which it is removed by filtration.

The amount of stabilized peptone solution which may be added to an electroplating bath is generally that previously employed in the prior art to prevent treeing and the formation of sprouts. Usually about 0.3 to 600, preferably about 8 to 120, milliliters per liter of stabilized peptone solution to the plating bath is added.

tElectroplating plating baths to which the stabilized peptone solutions of the present invention may be added are those which conventionally employ peptone to prevent treeing and formation of sprouts. Typically the metal may be tin, lead, zinc, copper, cadmium and mixtures thereof such as tin-lead. The baths may be alkaline such as a cyanide-type or pyrophosphate bath or the bath may be acidic such as a fiuoborate, sulfate, hydrochloride, acetate or sulfamate. An especially preferred electroplating bath to which the stabilized peptone solutions have been found elfective are the conventional tin, lead and tin-lead fluoborate baths wherein the metal content of thedeposit in the tin-lead bath contains approimately 1 to 99% tin and 99 to 1% lead. For instance, a tin-lead fluoborate plating bath may contain 14 to 250 grams per liter stannous fluoborate, 9 to grams per liter lead fiuoborate, 50 to 550 grams per liter fluoboric acid and 5 to 35 grams per liter boric acid.

In order to better understand the present invention the following examples are offered.

EXAMPLE I A peptone solution was prepared by dissolving about 300 grams of peptone in one 1) liter of water which was heated to about F. Stirring of the solution was continued until all of the peptone was dissolved. A series of one hundred (100) milliliter samples were placed in onehalf /2) pint clear glass bottles and various stabilizing compounds were added in an amount of approximately 20 ml./l. to each of samples. One bottle did not contain any stabilizer additive. The bottles were then capped. The compounds employed were paraldehyde, isopropyl alcohol, formaldehyde, acetic and formic acids. The sample containing no stabilizing compound decomposed within 48 hours at room temperature. After 14 days at room temperatures all of the samples containing stabilizing compounds were satisfactory and exhibited no visible bacterial growth.

To ascertain whether the stabilized peptone solutions had any adverse alfect on a tin-lead deposit deposited from a conventional 60/40 tin-lead fiuoborate plating bath, 20 mls. of each of the stabilized peptone solutions were added to one liter of a standard 60/ 40 tin-lead fluoborate plating bath. The plating baths were tested in a 267 ml. Hull Cell. All of the panels tested appeared satisfactory, indicating that the anti-bacterial agents did not have any adverse affect on the appearance of the tinlead deposits.

EXAMPLE II In this example four (4) 500 milliliter samples of peptone solution were prepared by adding 140 grams of peptone to about 300 milliliters of water and stirring without heating until no further peptone was dissolved. Each of the aqueous solution was then diluted to 500 milliliters and gently heated on a hot plate to about F. until all of the peptone was dissolved. Excessive heat was avoided to prevent thermal decomposition. The solutions were then cooled to room temperature in a cold water bath. The samples were designated A, B, C and D.

Sample A was stored in an amber colored bottle and kept at room temperature. It was found that within 48 hours the peptone solution decomposed due to bacterial degradation.

Sample B was also stored in an amber bottle and kept at 110 F. in a regulated oven. This sample decomposed within 24 hours due to bacterial degradation.

Samples C and D were also prepared as stated above, except that when these solutions were cooled to room temperature 5 milliliters of isopropyl alcohol and l rnilli-' liter of fluoboric acid were added to each of these 500 milliliter samples. The alcohol and acid were added to prevent bacterial decomposition. Sample C was stored at room temperature and Sample D was stored in an oven at 110 F. After seven (7) months standing under these conditions the stabilized peptone solutions of Samples C and D showed no evidence of bacterial decomposition.

EXAMPLE III In this example a series of plating tests were conducted with the stabilized peptone solutions to observe what effect, if any, these solutions had on a conventional 60/40 tin-lead deposit. It is known that the amount of peptone present in the bath has an effect on the percent tin in the tin-lead deposit. High peptone content in the bath would yield deposits higher in tin content. This factor was used to observe the degree of chemical decomposition which occurred, if any, to the peptone solutions employed.

Three 4-liter 60/40 tin-lead fluoborate plating baths were prepared using the following formulation:

250 milliliters lead fiuoborate 600 milliliters stannous fluoborate 72 grams boric acid 600 milliliters fluoboric acid Water to 4 liters Each of the above plating bath solutions had the following concentrations:

Sn+ 2 grams per liter Pb30 grams per liter HBF 100 grams per liter H BO 25 grams per liter The above plating baths were designated A, B, and C. To Bath A was added a freshly prepared sample of a peptone solution as prepared in Example II to give a concentration in the bath of about 5 grams per liter. No stabilizer was added. This was designated the control solution.

A stainless steel panel with an area of about 16.25 square inches was employed as the cathode in a 4-liter standard tin-lead fluoborate plating bath. This panel was plated at a current density of 30 amps per square foot for about 15 minutes to give a deposit on the panel of about 0.001 inch thick (1 mil). The deposit was removed from the stainless steel panel and chopped into A; inch squares. The tin and lead of the deposit were intimately mixed and a representative sample taken for analysis. The tin content of the deposit was 72.7%

Peptone solution Sample C prepared in Example II, containing isopropanol and fiuoboric acid as the sta bilizer additive Was introduced into the plating bath, designated Sample B, to give a peptone concentration in the bath of 5 grams per liter. The amount of solution added was 72 milliliters. Upon addition of the peptone solution to this bath a haze developed in the bath. The stainless steel panel used above was plated under the same conditions as used with Plating Bath A. The tin-lead deposit was analyzed and the tin content in the deposit was determined to contain 67.1%.

Bath B was then filtered through paper pulp to remove the haze and another stainless steel panel was plated under the conditions employed above. The tin content of the tinlead deposit was analyzed and determined to be 66.0%.

To the third plating bath prepared, designated Bath C, was added 72 milliliters of the stabilized peptone solution prepared in Example II, designated Sample D. Sample D was kept in an oven for seven months at 110 F. The concentration of the peptone solution in the plating bath was 5 g./l. The bath was filtered through paper pulp to remove the haze which had formed upon addition of the stabilized peptone solution to the tin-lead fluoborate plating bath. The tin-lead deposited on the stainless steel panel by the above procedure was analyzed and found to contain a tin content of 68.3%.

This example demonstrates that the stabilized peptone solutions, even upon standing for seven months, when added to a conventional tin-lead fluoborate plate bath resulted in tin-lead deposits which are acceptable.

What is claimed is:

1. A composition consisting essentially of an aqueous solution consisting essentially of peptone and from about 2 to 100 milliliters per liter of solution of at least one stabilizing compound selected from the group consisting of the following structures:

wherein n is an integer from 1 to 10; R is a member selected from the group consisting of hydrogen and an aliphatic or cycloaliphatic hydrocarbon radical from 1 to 6 carbon atoms; R is a member selected from the group consisting of a hydrocarbon radical from 1 to 6 carbon atoms and --OR; R is an aliphatic or cycloaliphatic hydrocarbon radical of l to 6 carbon atoms; and R is a member selected from the group consisting of R2, and

2. The composition of claim 1 which additionally contains 1 to milliliters per liter of fluoboric acid.

3. The composition of claim 1 wherein the peptone is present in an amount from about 50 to 500 grams per liter of solution.

4. The composition of claim 3 wherein the peptone is present in an amount from about 250 to 350 grams per liter of solution.

5. The composition of claim 4 wherein the stabilizing compound is present in an amount from about 5 to 50 milliliters per liter of solution.

6. The composition of claim 1 wherein the stabilizing compound is selected from the group consisting of alcohols, aldehydes and monocarboxylic acids.

7. The composition of claim 1 wherein the stabilizing compound is selected from the group consisting of isopropyl alcohol, formaldehyde, paraldehyde, formic acid and acetic acid.

8. The composition of claim 1 wherein the stabilizing compound is isopropyl alcohol.

9. An electroplating plating bath composition consisting essentially of about 0.3 to 600 milliters per liter of bath of an aqueous solution consisting essentially of at least one dissolved cationic electroplatable metal selected from the group consisting of tin, lead, zinc, copper and cadmium and having dissolved therein a peptone solution comprising peptone and from about 2 to 100 milliters per liter of peptone solution of at least one compound selected from the group consisting of the following structures:

wherein n is an integer from 1 to 10; R is a member selected from the group consisting of hydrogen and an aliphatic or cycloaliphatic hydrocarbon radical from 1 to 6 carbon atoms; R is a member selected from the group consisting of a hydrocarbon radical from 1 to 6 carbon atoms and OR; R is an aliphatic or cycloaliphatic hydrocarbon radical of 1 to 6 carbon atoms; and R is a member selected from the group consisting of R R OR and R OR -O-R 10. The bath composition of claim 9 containing as the metal a mixture of tin and lead.

11. The bath composition of claim 9 wherein the electrolyte is tin-lead fiuoborate.

12. The peptone solution of claim 9 which additionally contains 1 to 100 milliliters per liter of fluoboric acid.

13. The bath composition of claim 9 wherein the peptone solution is present in the bath in an amount from about 0.3 to 600 milliliters per liter of solution.

14. The peptone solution of claim 9 wherein the stabilizer compound is selected from the group consisting of alcohols, aldehydes and monocarboxylic acids.

15. The peptone solution of claim 9 wherein the stabilizer compound is selected from the group consisting of isopropyl alcohol, formaldehyde, paraldehyde, formic acid and acetic acid.

izer compound is isopropyl alcohol.

17. A tin-lead fiuoborate plating bath consisting essentially of an aqueous solution consisting essentially of about 9 to 110 grams per liter lead fluoborate, 14 to 250 grams per liter stannous fluoborate, to 35 grams per liter boric acid, to 550 grams per liter fluoboric acid and 0.3 to 600 milliliters per liter of a peptone solution containing 50 to 500 grams per liter peptone and 2 to 100 milliliters per liter of at least one compound selected from the group consisting of the following structures:

wherein n is an integer from 1 to 10; R is a member selected from the group consisting of hydrogen and an aliphatic or cycloaliphatic hydrocarbon radical from 1 to 6 carbon atoms; R is a member selected from the group consisting of a hydrocarbon radical from 1 to 6 carbon atoms and OR; R is an aliphatic or cycloaliphatic hydrocarbon radical of 1 to 6 carbon atoms; and R is a member selected from the group consisting of R R2O-'R2 and 18. The bath of claim 17 wherein the stabilized peptone solution is present in an amount from 8 to 120 milliliters per liter of solution.

References Cited UNITED STATES PATENTS 2,876,178 3/1959 McCoy 204-52 2,658,032 11/1953 Faust et al. 204-44 2,406,072 8/1946 Gaver 204'49 1,452,573 4/1923 Sirnkins 20454 2,271,209 1/1942 Schltitter 204-54 R 2,460,252 1/ 1949 Du Rose et a1 204-43 3,554,878 1/1971 Rothschild 204- 24 OTHER REFERENCES Metal Finishing, Guidebook 1966, pp. 252-253.

Metal Finishing, May 1966, pp. 77-79.

Organic Chemistry, 3rd ed., 1961, by Brewster et al., pp. 600 and 613.

Plating, December 1969, by Rothschild et al., p. 1366.

Metal Finishing, April 1966, by Subramanian et al., p. 56.

JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner US. Cl. X.R.

20444, R, 52 R, 53, 54 R CERTIFICATE OF CORRECTION Patent 3,647,652 Dated March 7, l9 7 2 Inventor) Nicholas J. Spiliotis It is certified that error appears in the above-identified patent and that said' Letters Patent are hereby corrected as shown below:

' .Claim 5, line 1, "4" should be -l.

Claim '9, line 2, "milliters" should be milliliters--.

Claim 9 line 7, 'milliters" should be --m illil:i. ters--.

Signed and sealed this 17th day of April 1973.

(SEAL) Attest EDWARD M. FLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

